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 HVAC systems consist of equipment, ductwork, and piping used to heat and ventilate buildings and to condition (cool and dry) the air.  Equipment can be: a furnace, an air- conditioning coil, a compressor, a plenum, a boiler, a tank, a pump, manifolds, outlets, and valves, etc…

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 The most common residential HVAC systems  Functions to cool and heat spaces  System consists of:  A furnace supplying heated air through ductwork  A main trunk line of rectangular duct  Supply lines running from the trunk line to the registers or vents  A return air duct returning the air from the rooms to the furnace  Metal duct using air between joists and studs.  See Fig 14.1 to Fig. 14.4

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 Determine the HVAC components needed for the residence in figures 14-1 and 14-2.  The furnace includes an air-conditioner.  A 2”X2” register is required at each base cabinet.  A 6”x 18” grille is needed at each return air.  Distance top of furnace to the roof is 20 feet.  The vent pipe is 4 inches in diameter.

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 Equipment: a furnace, a coil, a compressor, and a plenum (enclosed space to facilitate air circulation)  For the supply trunk: 16 feet of 8”x 12” rectangular duct, two 8”x 12” to 8”x 8” transitions, 17 feet of 8” x 8”, and two 8” x 8” end caps are needed.  For the individual supply lines 6-inch 90- degree elbow are needed

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 For the vents: 2 feet above the roof and 4 feet of pipe are needed; Two 4-inch 90-degree single-wall elbows, 4 feet of 4-inch-diameter single wall pipe, 22 feet of 4-inch-diameter double wall pipe, one 4- inch roof flashing, and one 4-inch termination cap.  One line set to connect the condenser to the coil, one thermostat, and one roll of wiring are needed.

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 Another type of residential heating  Uses hot water to warm the floor, which in turn warms the living space.  It consists of supply manifold, pump, boiler, return manifold, air ejector, expansion tank, and valves.  It cannot be used for cooling purposes  Figure 14-6 shows details about radiant heating

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 Small commercial buildings often use HVAC systems similar to that of the residential system, using more units as the building gets larger.  Larger single-story buildings often use a roof-top units (package units) that heat and cool the air and then distribute it through the building using ductwork.  As building gets taller a heat exchanger is used. The heating and cooling is accomplished by heating or cooling water at a central point.  Commercial systems may also use chillers, boilers, dampers, fans, and variable-air-volume (VAV) boxes.

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 Determine the HVAC components needed for the commercial HVAC system shown in Figure 14-8.  Two feet of 6-inch-diameter flexible duct is used to connect the diffuser to the ductwork.  The plenum is used for return air. The existing supply and return lines are made of copper.